Manufacture of electrical rectifiers



Patented Nov; 6, 1934 PATENT orrlcs MANUFACTURE OF ELECTRICAL RECTIFIERS Philip H. Dowling, Forest Hills, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application September 19, 1933, Serial-No. 690,080

Claims. (01. 175-366) My invention relates to the manufacture of electrical rectifiers, and particularly to the manufacture of the elements for rectifiers of the type disclosed and claimed in Letters Patent of the 5*United States No. 1,640,335, granted to 'L. O.

Grondahl on August 23, 1927. I

One object of my invention is to improve one step in the process of 'manufacture of the rectifier elements, whereby the electrical characteristics of the rectifier may be material improved.

I will describe one process of manufacture embodying my invention, and will then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1 is a view showing in elevation one form of blank ready to be prepared as a rectifier element in accordance with one process of manufacture embodying my invention. Fig. 2 is a view showing a number of blanks assembled on a support as they appear during one step in the process of manufacture. Fig. 3 is a view showing, invertical section, a rectifie'r element as it appears in one step in the process of manufacture embodying my invention. Fig. 4 is a view showing a completed rectifier element constructed in accordance with my invention.

Similar reference characters refer to similar parts in each of the several views.

Referring to the drawing, the reference character A designates a blank of suitable material such as copper. As here shown, this blank is of circular configuration and is provided with a central aperture 1, although this particular form is not essential. A number of these blanks are assembled upon a suitable support, here shown as a notched rod B of nichrome or other material unaffected by high temperature or the action of dilute nitric acid, the blanks being arranged in pairs in the notches as shown in Fig. 2, so that .A in contact. The blanks supported on the rod 3 in the manner shown are subjected to an oxidizing process, such for example, as the application of heat, to form upon the blanks a coating of a compound of the copper such as an oxide. The oxidizing process is continued until a sufiicient deposit of oxide is formed over the exposed surface of the blanks. The blanks will then appear as-shown in Fig. 3. It will be seen from an inspection of this view that blank A is'now covered with a coating D of cuprous or red oxide of copper, and outside of this coating is a thin layer C of cupric or black oxide of copper. It will also be seen from an inspection of Fig. 3 that the fiat face of the blank which is exposed during the oxthe blanks of each pair have their adjacent faces idizing process, that is to say the lower face has a much thicker oxide coating than the other face.

Following the oxidizing process, the blanks are cooled, usually by quenching them in water. The blanks are next well separated from oneanother and, if the water used for quenching purposes is tap water, they are dried by an air blast in order to prevent any impurities which may be present in the tap water from being deposited on, and adhering to, the blanks, where it might contaminate the solution used in the next step of the process.

After the blanks have been cooled and dried, they are treated with a solution which loosens the black oxide coating from the entire surface of the blank. For this purpose, I employ a dilute solution of nitric acid formed by adding distilled water to concentrated chemically pure nitric acid. This solution may have any desired concentration but a concentration of twentyfive per cent by volume or less is preferred. In order to prevent impurities from getting into the solution, the solution should be kept in a tank of material which is not attacked by the acid. The temperature at which the solution is used is not critical, and excellent results have been obtained at temperatures between 50 Fahrenheit and 68 Fahrenheit. I

The length of time the disks are immersed in the solution depends upon-the concentration and the temperature, although too long an immersion will decrease the efficiency of the disks. The best results are obtained when the disks have been immersed long enough to loosen the black oxide to such an extent that it still adheres to the disks after the disks are removed from the acid, 90 but that it will brush off in a powdery form when touched lightly with the fingers. As the acid solution weakens from use, the time of immersion must be increased.

Following the acid treatment, the disks are placed in a tank of running water and shaken vigorously to wash away any acid adhering to the disks. This rinsing will detach some of the black oxide but if it detaches most of it, it is a good indication that the time of immersion in 100 the acid solution may be decreased to advantage. If the rinsing water is tap water and not distilled water, any tongs or detachable handles used for handling the disks as well as the rods upon which the disks are mounted should be thoroughly cleaned by blowing the water off in an air blast or by rinsing in distilled water before these parts are again immersed in the acid solution. The disks may, ifdesired, be allowed to lie for a few minutes in a second tank of running water to be sure of the complete removal of acid.

In order to dry the disks after the rinsing operation has been completed, the disks are preferably strung on an unnotched rod loosely, but in such a way that they can touch each other, and a strong air blast is directed against their edges. This treatment will remove practically all'of the black oxide remaining on the disks. The disks will then appear as illustrated in Fig. 4, in which D designates the coating of cuprous oxide remaining on the inner. and outer edges of the copper blank and on one face A of the blank. It should be noted that the acid treatment not only removes all of the black oxide, but also some of the cuprous oxide, so that no oxide remains on the face A of the copper blank A.

The last step in the manufacture of the copper blank consists in rubbing finely divided carbon into the oxide coated surface of the blank. This may be done either manually or by a suit able machine such as is disclosed in Letters Patent of the United States No. 1,724,543, granted to D. G. Ackerly on August 13, 1929. While all of the black oxide will usually have been removed from the disks before this last step takes place, any remaining vestige of oxide will be removed by this step.

I am aware that dilute solutions of nitric acid have previously been used to remove the cuprous oxide from the copper blanks in the manufacture of electrical rectifiers, but in so far as I am aware, all of these solutions have been prepared by diluting the concentrated chemically pure nitric acid with ordinary tap water rather than with distilled water. One advantage of diluting the nitric acid with distilled water instead of with tap water is that the distilled water solution produces a disk having a cuprous oxide surface which is smooth enough to give no trouble in the carbonizing process and yet sufliciently rough to take the carbon well, while the tap water solution frequently produces disks with very rough cuprpus oxide surfaces which are very diflicult to carbo ize and which make the disks hard to handl in any self-feeding device such as an automatic testing machine.

A further advantage of using a distilled water solution of nitric acid instead'of a tap water solution is that the tap water solution nearly always leaves a deposit of metallic copper on the cuprous oxide surface, whereas the distilled water solution leaves no visible metallic copper on the cuprous oxide surface if the solution has the proper concentration. Furthermore, any metallic copper which may be deposited on the cuprous oxide surface of the disks during the use of a distilled water solution adheres so lightly that it may be removed by a brisk rinsing in water followed by an air blast directed against the edges of the disks after they are strung on a rod following the rinsing process.

Although I have herein shown and described only one process of manufacture embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I 'claim is:

which consists in heating a copper blank to form thereon a coating of cuprous oxide and an outer coating of cupric oxide, and then immersing the blank in a nitric acid solution having any concentration up to 40% by volume just long enough to loosen the cupric oxide from the cuprous oxide sufliciently to permit its ready removal from the cuprous oxide by mechanical means, said nitric acid solution being formed by adding concentrated chemically pure nitric acid to distilled water.

2. The process of preparing a rectifier unit which consists'in treating a copper blank to form thereon a coating of cuprous oxide and an outer coating of cupric oxide, and then immersing the treated blank in a dilute solution of nitric acid formed by adding concentrated chemically pure nitric acid to distilled water, saidblank being immersed in the nitric acid solution long enough to loosen the cupric oxide from the cuprous oxide but not long enough to actually remove the cupric oxide from the cuprous oxide.

3.-The process of preparing a rectifier unit which consists in treating a copper blank to form thereon a coating of cuprous oxide and an outer coating of cupric oxide, and then immersing the treated blank in a solution of nitric acid having a concentration of 25% or less by volume long enough to loosen the cupric oxide from the cuprous oxide but not long enough to actually remove the cupric oxide from the cuprous oxide, said solution of nitric acid being formed by adding concentrated chemically pure nitric acid to distilled water. I

4. The process of preparing a rectifier unit which consists in treating a copper blank to form thereon a coating of cuprous oxide and an outer coating of cupric oxide, loosening the cupric oxide from the cuprous oxide without actually removing the cupric oxide from the cuprous oxide by immersing the oxidized blank in a dilute solution of nitric acid formed by adding concentrated chemically pure nitric acid to distilled water, washing the blank in water to remove the acid, and finally directing a strong air blast against the side of the blank to remove the cupric oxide from the cuprous oxide. 1

5. The process of preparing rectifier elements which consists in supporting/fiat metallic copper blanks in pairs with adjacent faces in contact on a support which is unaffected by high temperature and nitric acid, heating the blanks to form a layer of cuprous oxide-and an outer layer of cupric oxide on the blanks, cooling the blanks by quenching them in water while still on the support, drying the blank with an air blast to prevent impurities from the water from adhering to the blanks, loosening the cupric oxide from the cuprous oxide without .actually removing it from the cuprous oxide by immersing the support and blanks in a dilute solution of nitric acid formed by adding concentrated chemically pure nitric acid to distilled water, washing the acid from the blanks by immersing the support and blanks in running water, removing the blanks from the support and supporting them on another support loosely in such manner that they can touch one another, and finally directing a vigorous air blast against the'edges of the blanks to detach the cupric oxide from the cuprous oxide. 

